Means for compensating for liquid volume variations in hydraulic remote control systems



Nov. 3, 1953 2 657,536

R. L. LEVY 2 MEANS FOR COMPENSATING FOR LIQUID VOLUME VARIATIONS Filed May 5, 1947 IN HYDRAULIC REMOTE CONTROL SYSTEMS 2 Sheets-Sheet 1 INVENTOR %WOOMW MA ATTORNEYS Nov. 3, 1953 R. LEVY ,53

MEANS FOR COMPENSATING FOR LIQUID VOLUME VARIATIONS IN- HYDRAULIC REMOTE CONTROL SYSTEMS Filed May 5, 1947 2 Sheets-Sheet 2 INVENTOR "Levy 0 ATTORNEYS Patented Nov. 3, 1953 MEANS FOR COMPENSATING FOR LIQUID VOLUME VARIATIONS IN HYDRAULIC RE- MOTE CONTROL SYSTEMS Ren Lucien Levy, Paris, France, assignor to Societe dlnventions Aeronautiques et Mecaniques S. I. A. M., Geneva, Switzerland, a corporation of Switzerland Application May 5, 1947, Serial No. 746,031 In France July 31, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires July 31, 1962 7 Claims.

The present invention relates to hydraulic remote control systems.

More particularly this invention relates to hydraulic remote control systems of the type in which a transmitting station imparts, through a double hydraulic circuit, movement to a driven member at a receiving station.

Hydraulic remote control systems are known which incorporate means that compensate for leakage and also systems are known which provide means for maintaining synchronism between the movement of the driving and driven members.

Accordingly, the present invention has for an object to provide a hydraulic remote control system of the type including a transmitting and a receiving station anda double hydraulic circuit between the stations with means for compensating for variations in the liquid volume in the circuits.

Specifically the remote control system of the present invention provides means which permit the expansion and contraction of the liquid in the fluid circuit to occur at all positions of the respective driving or driven members in the system so that the component structural parts of the control system are in the proper operating conditions regardless of any temperature changes that may afiect the liquid. This is particularly true as regards an increase in temperature since such an increase has an efiect of causing a compression in the channels or ducts of the system and thereby necessitating an increased component of the driving force that may be out of proportion to the resistance established by the driven member.

Still more specifically, this present invention provides a hydraulic remote control system which, while incorporating means allowing for 'free expansion and contraction of the liquid volume in the system, also provides a system which is capable of transmitting powerful driving impulses and still maintain synchronism between the driving and the driven member at the respective transmitting and receiving stations.

In order to accomplish the aforegoing objects, it is a still more specific object of this invention to provide in conjunction with the remote control system a container or tank for liquid with conduit means providing communication between the respective stations and this container so that the entire hydraulic circuit can communicate with the container. The system is provided with valve means associated with the transmitting station which close communication between the 2 container and one of the hydraulic circuits prior to the initiation of a power transmitting movement or stroke and during the duration of such stroke.

structurally the present invention has for an object to provide at a power transmitting station a cylinder, a double headed piston within the cylinder and between the heads of the power transmitter piston, power transmitting means which is operably connected for movement responsive to the movement of the driving member. The heads of the power transmitter piston are provided with ports and the power transmittin member constitutes a valve body and has means normally maintaining the same in spaced relation to both of the ports so that except during the power transmitting period there will be communication between the heads of the power transmitter piston and the space beyond the heads. In this connection the power transmitter piston has less axial extent than the axial extent of the cylinder at the transmitting station. This space between the heads of the power transmitter piston is in communication with the liquid tank.

It is a further specific object to provide in a remote control system of the type incorporating a transmitting and a receiving station each in-- cluding a piston and cylinder arrangement in which the respective cylinders have a greater axial extent than the pistons within the same and the pistons are more than half the length of the cylinders and in which each piston is a double headed piston provided with ports through the heads thereof, a fluid volume compensating means which includes a tank for containing liquid and conduit means externally of the cylinders and communicating with the same medially thereof so as to provide constant communication between the tank and the space between the heads of the pistons, a double hydraulic circuit including conduits connecting the respective opposite ends of the cylinders and valve means associated with the ports in the heads of each piston includin valve means associated with the transmitter piston opening toward the space between the heads of the piston and valve means associated with the ports of the receiver piston opening away from the space between the heads of this receiver piston.

Consistent with the aforementioned object, the invention has for an object to provide in conjunction with the receiving station, the double headed receiver piston of less axial extent than the receiver cylinder, ports through the heads of the receiver piston and valve means including stems extending through the ports and terminating within the space between the heads of the receiver piston so that the valves in the respective heads open away from one another and thus toward the space beyond the heads of the receiver piston.

Still more specifically, it is an object to provide in cooperation with the valve stems immediately aforementioned a stationary abutment within the receiver cylinder that is contacted by either valve stem depending on the direction of movement imparted to the receiver piston to open the valve, the stem of which has contacted the abutment to permit fluid to flow from the 1 space beyond the head of the piston, the valve stem of which has contacted the abutment, to the reservoir and vice versa so as to insure synchronism between the position of the driven member with respect to that of the driving memher at the completion of the power transmitting stroke Further and more specific objects will be apparent from the accompanying drawings, in which:

Figure 1 diagrammatically illustrates one form of hydraulic remote control system incorporating a movable power transmitting member that functions as a valve body associated between the heads of thepower transmitter piston,

Figure 2 illustrates diagrammatically and in lon itudinal section anembodiment of the invention,

Figure 3 is a transverse cross-sectional View taken medially through a power receiver piston I and cylinder arrangement and illustrating the preferred shape of the means that operably connect the receiver piston with the driven member, and

Figure 4 is a sectional view taken on lines 4-4 of Figure 3 and illustrates a one-way drive connection for the driven member.

In the drawings, in Figure 1 the reference character ze denotes the power transmitting station and B denotes the receiving station, each of these stations being constituted by a cylinder wit which is e e v ly mov ble r m ter piston and a receiver piston. llhe opposite ends of the transmitter cylinder and receiver ylind r a conn t by conduit means externally of the cylinders, G and C and which condu means cons a doubl h raul Circuit or connection between thestations. The power transmi er pi t n iso uble he ded piston nd includes opposite head P and B Itistobe noted that bo h power t ansm er nd receiver pistons are respectively of less. axial extent than the axial extent of their associated cylinders but that each are approximately more than half the length of the cylinders. The space between the heads of the power transmitter piston is denoted by reference character M and a liquid containing tank R is in communicationthrough suitable duct or channel with this space M substantially medially of the length of the cylinder at the transmitting station A. Disposed between the heads P and P of the power transmitter piston is a power transmitting member L which is of less axial extent than the distance between the heads P and P so that it constitutes a slider mounted with a limited play within the space or chamber M. A driving member a is operably connected to the power transmitting memberL. At the receiving station B is a receiver piston Q to which is operably connected a driven member I and which receiver piston Q moves responsive to the impulses transmitted by the movement of the piston at the transmitting station.

The heads P and P of the power transmitter piston are provided with ports or ducts 2 29 respectively providing communication between space or chamber M and the chambers d and cl beyond the heads of the transmitter piston. These ducts or ports p and p open into the space M respectively opposite the end faces Z and Z of the power transmitting member L. This power transmitting member L constitutes a double valve body and within the faces Z and Z are mounted packing plugs g and g which cooperate, depending on the movement of the body L with the ports 11 and p to close the same.

' Thisarrangement operates as follows: If the valve body or power transmitting member L is moved to the direction of arrow f responsive to movement of the driving member a, the packing plug g in the face Z? of the body L bears against the end of the port 'p 'to close the same". its power transmitting movement continues the double valve body L drives the power transmitter piston to the right as shown in the drawings so that liquid passes from chamber (1? throughconduit G into chamber q? at the receiving station to initiate movement in the direction of the arrow f3, to the left, as viewed in thedrawing. in the receiver piston Q and thus .a corresponding movement is imparted'to the driven member 1?, the liquid in chamber q. 'at the receiving station passing through channel 0 into chamber d Any expansion or contraction of the liquid in the system is compensated for substantially in,- stantaneously due to the transfer of liquid between the reservoir ;or tank R and the particular hydraulic circuit either 0 or C through the ports p or p provided that the. openings of the ports are uncovered due to the position orthe body L within the space between the heads of the transmitter piston.

It is thus clear that an expansion in either circuit C? or C will permit fluid to flow back through port p or 23 respectively, into the space M and thus to the reservoir.

In Figure 2, the transmitting and receiving stations are denoted respectively at A, B. At the transmitting station is a cylinder I within which is mounted a transmitter piston 2. The piston 2 is a double headed piston having Spaced opposite heads 3' and 4 interconnected by a ro portion '5. The axial extent of the double headed piston 2 is, as indicated, less than the axial ex.- tent of cylinder I but more than half of the axial extent thereof. The heads 3 and 4 delimit between them a central chamber or space 6. Beyond the heads are additional chambers! and 8, the fluid chamber 1 being comprised between-the outer face of the head 3 and the adjacent cylin: derwall and the chamber ,8 being comprised lootween the outer face of the head 4 andthe inner space of the adjacent wall.

The receiving station B is also constituted by a cylinder 9 within which is movable a receiver piston including spaced heads H and I2 interconnected by a rod portion I3. The receiver piston Ill including its heads has an axial extent less than that of the cylinder 9 but more than half the length of the cylinder 9f The space between the heads H and I2 constitutes acham ber l4, while between t outer face or head H and the adjacent cylinder end wallis a chamber I5 and between the outer face ofpiston head i2 and the adjacent cylinder end wall is a chamber I 6;

A double hydraulic circuit is included in this system including the conduit I'I', externally of the cylinders and interconnecting chambers 8 and I5, and another conduit It also externally of the cylinders and interconnecting chambers I and It. The conduits I! and I8 constitute a double hydraulic circuit denoted generally at C.

Within the space or chamber 6 between the heads 3 and A of the power transmitter piston is mounted a slidable power transmitting member I9. This member I9 constitutes a double valve body and has operative end faces 25 and 22 which can be made of plastic or rubber and which, as shown, are maintained in spaced relation with respect to the adjacent faces 25 and 25 of the piston heads by spring means 20. In other words, the power transmitting member l9 has less axial extent than the space l'etween the piston head faces 25, 28 and the spring means at the opposite ends of the power transmitting member I9, that are mounted respectively between faces 2! and 25 and 22 and 26, tend to maintain the power transmitting member I9 centrally of the space 6. The heads 3 and 4 are bored through to provide ports or ducts El and 28. Packing rings 23 and 24 surround the ports or ducts 21 and 28 respectively and cooperate with the end faces 2| and 22 upon movement of the power transmitting member I9 to right or left depending on the direction of movement imparted thereto.

On the upper face of the power transmitting member I9 is a toothed rack 33 that cooperates with a cog Wheel denoted diagrammatically at 38 constituting a rack and pinion arrangement. Thecog wheel 38 is locked on the shaft 39 upon which is mounted the lever 49 that constitutes the driving member. It is thus clear that movement of lever 48, through the interposition of cog wheel 38 and rack 3'! moves power transmitting member I9 accordingly.

At the receiving station, the piston heads Ii and I2. are likewise drilled through to provide ports or ducts M and 42 respectively. These ports are respectively controlled by flap valves 43 and 44, the stems '45 and 36 of which extend through the ports 4i and 12 and terminate in the space M between the heads II, I2 of the piston I9. washers 41 and t8 and are surrounded by springs 49 and 5s interposed between the washers and the adjacent piston head faces which normally bias the valves 43 and M to closed position. A

stationary abutment Si is mounted within the space It substantially medially of and symmetrical with respect to the mean transverse plane of cylinder 9 so that it is in the path of movement of the valve stems 35 and 26. The rod or member I3 that interconnects the piston heads II, I2 is U-shaped in cross-section so that the opposite legs of the U pass down on opposite sides of the stationary abutment 5| as indicated with reference to the arrangement of Figure 3. The upper surface of the member I3 is provided with teeth 52 with which cooperate the teeth of a cog wheel 53 so that movement of the receiver piston imparts movement to the wheel 53 and thence through a one-way or non-reversible coupling denoted diagrammatically at 55 of the type as described with reference to Figures 3 and 4, to the lever 56 constituting the driven member. This coupling'is such that the movement of the receiver piston moves the driven member 54, but the reverse movement, that is movement of the These stems are respectively provided with 6 driven member, does not react back on the re ceiver piston.

Figures 3 and 4 illustrate a portion of the receiving unit of slightly modified form and on a diiferent scale than the illustration in Figure 2 with particular reference to the coupling or nonreversible drive transmitting means between the driven member and the receiver piston. In Figure 3 the cog wheel 53' is locked on a shaft 56. This shaft passes transversely through the receiver cylinder 62 and a conduit, a portion of which I3 provides communication with the space between the heads of the receiver piston, and a tank or reservoir for liquid similar to the tank "II of Figure 2. A stationary abutment 5! is mounted medially of the bottom of receiver cylinder 52 and cooperates with the heads of the receiver pistons in this cylinder. The power receiving member within the receiver cylinder 62, that is the rod I 3' that extends between the heads of the receiver piston, is U-shaped in section as shown and provided with teeth on its upper surface for cooperation With teeth on the wheel 53'. It thus follows that movement of the receiver piston imparts movement to the wheel 53' and thus to shaft 56. On shaft 56 are a plurality of fingers 51, four as illustrated in Figure 4. These fingers engage with clearance, projections 58, two of which are shown, that are mounted on a disk 59. This disk 59 has a tubular extension 60 and is journalled for free rotation about shaft 56. The disk 59 is mounted within an annular crown 5| that forms part of the casing of receiver cylinder 62. This crown BI is therefore fixed. Inclined planes 63 and B4 are provided on opposite faces of the disk 59 and ball members 65 and 65 are mounted on these inclined planes, spaced apart by spring means 68 disposed between two out-turned ends 59 and Iii of fingers 5?. These balls65 and 56 are normally pushed into the angles of the internal periphery 57 of the annular crown and the respective inclined planes 63 and 64. The driven member 5 3' is locked for rotation with the tubular extension 60.

It is therefore clear that, while shaft 56 is capable of driving responsive to its rotation, in one or the other direction, the disk 59 and thus driven member 5 3', the first phase of motion of shaft 55 interrupts the wedging action of the balls, but a reverse rotation, that is starting from driven member Ed, is not possible since the balls are wedged.

In both forms of this invention the receiver and transmitter cylinders communicate with the storage container or reservoir. In Figure 2 the reservoir H is connected via pipes I2 and 73 at points medially of the length of cylinders I and 9 so that there is always fluid communication between the central chambers 6 and I4 and the reservoir II.

In the operation of the invention, with reference to Figure 2, if lever 40 is turned to the left in the direction of arrow f, the slidable power transmitting member I9 is displaced to the right in the direction of arrow f and during th first phase of this motion the operative face 22 of member I9 is applied against packing ring 24, if this face was not already against this ring due to the conditions of the liquid, and thus duct or port 28 isclosed. As movement of lever 40 is continued, the transmitting member I9 drives piston 2 to the right in cylinder I. The portion of the liquid in chamber 8 is forced by the head 4 of transmitter piston through conduit Il into to s sec qna a a o c lin ers and. h s t e seaweed, h m ans h Q e ablr conn c th rowe ransm tt ns rsi -li e t with th l er 4.9 and t e rod. m mber t w th he ver 5% bein essential s mila thc movem at dri i g; cesr b o jve it is uplicated b h riven rc mi ther i n xpan ion r; ontrac i n i he liqu d-due o iat ons of tempe ature, i substantiel y me iat y compen ated o by tansie oi id be we n h res vo r 11 and e P per ch be i the res c ve X FlQ FS: It, hen t i ex a s on. s r-c tra on oc urs. the power ransm ember I s s a ed 2 m the iiiston heads 3 nd s, h O tl s o o 21- and .2 are open. and iquid t an its c urs i iv th h ha b r 6-. f. on o he en aces 21 art-lot powe transm ttin member is s applied a nst, the ad ac nt face of a. pist n head. s ch a ac 4: b in ap li d a ain fa e 25., pressure oi. he liquid. in amb r increasin by expansi movcspower tr nsm ttin -m m er it; away, s to. its osi n c ntr ly f ham e 6;, so as to op n po t 21- A contraction of the liquid in the system can ause. th penin of valves is. and M at the re.- ceiving station B. against the action of springs Q9, and and the required resupply of liquid passes from tank H into the aliected hydraulic circuit I]: or t8 and the associated chambers 8. and l. I: or I and it, respectively.

Since the springs. assign a definite position to the driving member or lever lli as regards the position of the power transmitting member 2, as soon as driving lever is released by the op:

erator, the synchronism between the position of the driven member 54. and the position to. which the driving member or lever All can be displaced is insured in an accurate. manner. In the event the. displacement or the driven member 5A establishes only a slight resistance, power transmission is. effected. Without any substantial clearance ex-. isting between faces 2t and 21 and 25. and 2.6 since the face 2| is slightly pressed against the packing rings 23 and 24 and the. distances between faces 25- and 26 ofpiston heads 3 and 4 and faces. 2t and 22 of the transmitting member t8 remain substantially constant.

It there, is any leakage in the system it is com.-. reheated LQ Z by de ve y f quid rom th one tailileig H and thence through either circuit or conduits IT or l8 and through the ports throughp s on hea s H and F lrths -m ra if o y ea on. h position ct g member or lever 40 and driven member 5A are. no longer in synchronism, a resynchronizae tion is effected by a to and fro movementof the driving lever 40. If, for example, upon rotation of the driving level 5.0; in the direction of'the ar FQW J, the driven member 54 is moving out. 0t phase or is leading the, movement of the driving member, the receiver piston l0, reaches. the end; Qt s. tro e efo t e. t sm t r pis on has reached the end of its stroke. Thus, when the receiverpiston ll] reaches the endof its stroke, valve stem contacts abutment 5| and, valv is. open d that or the remai in -period f m tion of transmitter piston 2, the liquid expelled rom. chamber?! passes throu h port M nt t sp e. e wee p onhcads it and 1:2. and thenc t r u h. con uit 13. i to the tank H:- When the transm tt r pis .2. has reached th and tit stick th tw pistons are a ain in sy ch E sicabl-y th conduits 12 and 13. communicate w h he oo of chambers t and 545 so as to auto ma ical y ro de. for any substantial. increase in p essure The essence. of the present. invention consists s em. for compensating for liquid volume variationsin combination with means providin 9 res nchronization of the. receiver with the transmitter, As set forth, the invention is; char-1 acterized by the fact thatv the transmitting and tefieivingstations areleach provided with a valve s em an that the valves in each system open opposite directions, in other words they com-1 municatio between chamber a and chamber .6. is normally open while the communication between chamber 1 5, and chamber 16 is. normally closed. '{Ifhus expansion of fluid occurring; in line, H i absorbed by passage through conduit 28. into chamber 6: and, return d o the tank. and as. soon as contra on o urs liquid flows past valve 43. from the chamber 14;. Additionally, the valves 43 and 44 w h n. oward he chambers,

nd. it o at th. th fired ab tment- 5!;

so if for any reason the position or the element an f the lever 54 are ut of. phase, resyn h iza n is ned by hack and forth movement ofthe element 4.0,, If for nstancathe Pee ceiver piston Ii} has for any reason reached the end o s st oke. e ore the. power transmitter piston 2 has reached the end of its stroke, stem 45 contacts the. abutment, opens valve 43. so that during the remainder of the stroke ofv the unit 2* the liquid flows from chamber 8: past valve 43 and back to the tank.

What I claim is;

1. In a hydraulic remote controlsystem of the type includinga transmitting station and a receiving station, movable drive means at the. transmitting station for initiating a, power stroke; in opposite directions, driven means at the. receiving station movable in response to themove merit oi? the drive means, each station including a double ended cylinder respectively constituting a transmitter cylinder and a receiver cylinder, a double. headed. piston movable in each cylinder and respectively constituting a transmitter piston and. a receiver piston, each piston having an axial extent more than half the axial extent of its associated cylinder and less than the total axial extent thereoi', conduit means external-ly of the cylinders and respectively providing com-. munication between the opposite ends of the cylinders, and means operably connecting the driven means with the receiver piston, the improvement comprisinga fluid volume compensatthe tank, conduit means connecting-- the tank incomm-unicat-ion with each cylinder at a point lying medially of the length of each cylinder so that the tank is always in fluid communication with the cylinder atthe space between the heads ofthe pistons therein, a movable power transmitting member disposed between the heads of the transmitter piston, means operably. connecting the drive meanswiththe power transmitting member so that movement of; the drive means moves. th power transmittina me ber. and; hus. the t ansmit a oiston. to; orc l id to the r Qe iv vli d to i tiate mov ment oi th e ceiver piston and thus the driven member, ports through each head of each piston and providing communication between the opposite ends of each cylinder and the space between the heads of each piston and valve means at the heads of each piston controlling communication through the ports.

2. In a hydraulic remote control system of the type including a transmitting station and a receiving station, movable drive means at the transmitting station for initiating a power stroke in opposite directions, driven means at the receiving station movable in response to the movements of the drive means, at each station a double ended cylinder respectively constituting a transmitter cylinder and a receiver cylinder, a double headed piston movable in each cylinder and respectively constituting a transmitter piston and a receiver piston, each piston having an axial extent more than lialf the axial extent of its associated cylinder but less than the total axial extent thereof, conduit means externally of the cylinders and providing communication between the respective opposite ends of the cylinders, and means operably connecting the driven means with the receiver piston, the improvement comprising a fluid volume compensating tank, additional conduit means extending between the tank and the cylinders and in communication with each cylinder at a point lying medially of the length thereof so as to always provide communication between the tank and the space between the heads or the piston at each, station, a movable power transmitting member disposed between the heads of the transmitter pistons, ports through each head of each piston providing communication between the opposite ends of each cylinder and the space between the heads of each piston, valve means at the heads of each piston for controlling communication through said ports, said movable power transmitting member constituting the valve means at the transmitting station, means normally spacing said transmitting member from both heads of the transmitter piston, means operably connecting the drive means with the power transmitting member so that movement of the drive means moves the power transmitting member and thus the transmitter piston to force fluid into the receiver cylinder to initiate movement of the receiver piston and thus the driven means, and said transmitting member being operably in a power transmitting stroke to move to a position closing one of the ports in the head of the transmitter piston before imparting power transmitting movement to said transmitter piston, and said transmitting member maintaining the said port closed during the duration of power transmitting movement.

3. In a hydraulic remote control system of the type defined in and by claim 2, and in which the means for normally maintaining the transmitting member spaced from both heads of said transmitter piston constitute spring means.

4. In a hydraulic remote control system of the type defined in and by claim 2, in whichthe means for normally maintaining the transmitting member spaced from both heads of said transmitter piston constitute spring means, and the valve means at the heads of the receiver piston constitute normally closed valves carried by the receiver piston and including valve heads cooperable with the respective heads of the receiver piston at the faces thereof adjacent the ends of the receiver cylinder, valve stems pro- 10 jecting through the ports in the heads of the receiver piston and terminating in the space between the heads of the receiver piston, and spring means for normally holding said last mentioned valves closed.

5. In a hydraulic remote control system of the type defined in and by claim 2, in which the means for normally maintaining the transmitting member spaced from both heads of said transmitter piston constitute spring means, the valve means at the heads of the receiver piston constituting normally closed valves carried by the receiver piston and including valve heads cooperable with the respective heads of the receiver piston at the faces thereof adjacent the end of the receiving cylinder, valve stems projecting through the ports in the heads of the receiver piston and terminating in the space between the heads of the receiver piston, spring means for normally holding said last mentioned valves closed, and a fixed abutment disposed substantially centrally of and within the receiver cylinder and in alignment with the path of movement of the valve stems carried by the receiver piston whereby depending on the direction of movement of said receiver piston one of said valve stems contacts said abutment to open communication through the port controlled by the valve, the stem of which has contacted the abutment so as to provide communication between the space between the heads of the receiver piston and the space beyond the head carrying the contacting valve stem so as to'provide for synchronization of the movement of the receiver piston with respect to the movement of the transmitter piston and also to permit resynchronization of the receiver piston.

6. In a hydraulic remote control system of the type including a transmitter, a driving means for initiating movement in opposite directions thereof, a receiver, a driven means responsive to the movements thereof, said transmitter including a double ended transmitter cylinder, a double headed transmitter piston movable in said cylinz der, having an axial extent less than the axial extent of the transmitter cylinder but more than half the axial extent thereof and the heads of said transmitter piston being spaced from one another, said receiver including a double ended receiver cylinder, a double headed receiver piston movable in said receiver cylinder and also having an axial extent less than the axial extent of the receiver cylinder but more than half the axial extent of the receiver cylinder, the heads of said receiver piston being spaced from one another, means operably connecting the receiver piston to the driven means, a double hydraulic circuit between the cylinders including conduit means connected between and respectively providing communication between opposite ends of the cylinders, each head of each piston having a port therethrough through which fiuid can flow in the cylinders between the space beyond the heads of each piston and the space between the heads of each piston, a fluid volume compensating tank, conduit means externally of the cylinders connected to the tank and in communication with each cylinder at a point substantially medially of the length thereof so as to provide constant fluid communication between the tank and the space between the heads of each piston, a movable power transmitting member between the heads of the transmitter piston, means operably connecting said driving means with said movable power transm irils member so that movement of, the dr ivmeans normally maintaining the transmitting member spaced from the ports in the heads ofv the transmitter piston so that upon movement of the driving means ina power transmitting stroke in either direction said power transmitting member moves to first close fluid communication between the space between the head otthe transmitter piston and the adjacent end of' the transmitter cylinder toward which the power transmitting movement is directed and thence to move said transmitter piston so as to force fluid to flow into the; end of the receiver cylinder that is in fluid communication with the said adjacent end of the transmitter cylinderto impart movement to the receiver piston and thus. to the driven means in correspondence with the movement of the driving means, and normally closed valves controlling fluid flow through the ports in the heads of the receiver piston and movable to open position in response to contraction of fluidvolume in the hydraulic circuits between and includingthe cylinders so as to permit fiuid'to flow from-the tank to the space between the heads of the receiver piston, through the ports in the heads of the receiver piston and into. the circuits.

'7. In a hydraulic remote control system of the type defined in and by claim 6', in which the means for, normally maintaining the transmitting member spaced from both-heads of said transmitter piston constitute spring means, the valve means at the heads of the receiver piston constituting normally closed valves carried; by the receiver piston and. including valve heads cooperable with the respective heads of the receiver piston at the faces thereof adjacent the.

ends of the receiving cylinder, valve stemsprojecting through the ports in the-heads of the receiver piston, spring means for normally holding said last mentioned valves'closed, and a fixed abutment disposed substantially centrally of and within the receiver cylinder and in alignment with the'path of movement of the valve'stems carried by the receiver piston whereby depend ing. on the direction of movement. of said receiver'piston one of said valve stems contacts said abutment to open communication through the port controlled by the valve, the stem of which has contacted theabutment so as tov provide communication between the space between the heads. of the. receiver piston and, the space beyond the head carrying the contacting valve stem so as to provide, for synchronization of'the vmovement of the, receiver piston with respect to the movement of the transmitter piston and also to permit resynchronization of the receiver piston.

RENE LUCIENLEVY.

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